How to get rid of an indoor spider mite problem
May 12, 2019 11:03 AM   Subscribe

I have a lot of plants in my apartment. Some of my big boys have spider mites - most notably, two types of larger banana plants. For the past year I've been trying to control it - mostly with wiping down the leaves / spraying water on them daily-ish. But the mites are still there! Help!

I've also tried a few "natural" miticide sprays, and those did jack shit. Cold water works better. But I want to get rid of these plant-ruining assholes, and I'm at the point where I'm willing to go nuclear.

What are some hard-core miticides I can use indoors? And has anyone had luck with predatory mites? Has anyone invented mite-killing nano-bots yet?

I sometimes bring the banana plants outside and spray them down with a hose, but I only have a balcony so my outside options are limited. (Hose comes from the sink, balcony is about 100 sq ft.) That being said, I'm once again hosing them down outside because in the past 2 weeks the mites exploded, despite my constant vigilance with a water sprayer and a rag.

Thank you in advance.
posted by weed donkey to Home & Garden (8 answers total)
Response by poster: My other indoor plants that have this spider mite problem: the Anthurium, the Money Tree, the Parlor Palm, and the False Aralia.
posted by weed donkey at 11:12 AM on May 12, 2019

Spinosad is a bacteria-derived pesticide that doesn't appear to pose health risks to humans and is certified for organic production; it can be found in products like Monterey Garden Insect Spray. With repeated applications I've found it to be very effective at controlling spider mites, but only when the infestations aren't yet bad enough to form webs on the undersides of the leaves; maybe try it after wiping down the plants. The main drawbacks are that it can kill beneficial insects, particularly posing a risk to to pollinators when applied to flowers, and that (anecdotally) spider mites can develop a resistance when it's used heavily and for a long period of time.
posted by Rust Moranis at 11:12 AM on May 12, 2019

You don't want to hear this, but: the only way I have ever personally brought spider mites under control indoors is to stop growing the plants they seem to find most delicious (including bananas, parlor palm, and most of the Araliaceae[1]). "Natural" sprays, hand-wiping, and over the counter miticides sometimes helped, but never actually eliminated the problem.

The good news is that throwing out the badly infested plants spared some of the others -- I was able to keep my Anthuriums, for example.

I did see some benefit from taking plants into the bathtub and spraying them with a detachable showerhead on a less-gentle setting (like "pulse" or "massage." It may take some experimentation to find a setting that works without punching holes through the leaves.), especially in combination with misting with soapy water. (Little bit of dishwashing liquid in water, mist on all surfaces of the plant, wait a couple minutes, power-rinse with water, let drain, hand-wipe optional. Do every time the plant needs water.)

Outdoor predators may take care of the problem for you to a degree, if you can leave the plants outdoors for the summer, but that may or may not be a viable solution depending on your location, the size of the balcony, and the direction it faces.

Direct sun makes spider mite problems worse, as do dry air and heat. You could try moving them to a cool, moist location out of direct sun if you have one, and continue with the hand-wiping, soap, power-washing, etc., for six weeks or so. The banana won't like that, but if you explain that the only other option is the landfill, it might accept it. You might see some benefit to just moving plants a foot further away from the window.

I have tried predatory mites for a different indoor pest problem (thrips in my case), and they did jack and shit. (My theory is that most of the mites they sent me were not actually alive when they got here, but I can't prove anything, and it was an expensive enough experiment that I've never wanted to try again.) If you have the money, and / or you love the plants enough, you can try predatory mites and see how it goes. I do know people who say that they've had success from predatory mites for indoor pest problems; I'm just not part of the club myself.[2]

Obviously if you do predatory mites, you can't also do the soapy water / hand-wiping / power-wash stuff for however long it takes to determine whether the predatory mites are doing anything, which might mean that the problem gets a lot worse before it gets better, and might mean that the problem just gets a lot worse.

The nanobot thing sounded promising at one point, but the documentaries I've seen on TV make it sound like they're all just one tachyon pulse away from developing sentience, and then you either have to grow spider mites for them forever, or live with the guilt of destroying a whole civilization.


[1] Which, confusingly, includes false aralia (Schefflera elegantissima, formerly Dizygotheca elegantissima).
[2] One of the problems, too, is that predatory mites are mainly intended as a solution for outdoor pest problems, and indoor conditions will not necessarily be what the predatory mites will find most comfortable. So even if you get living, hard-working, hungry mites in the mail, they might not like your place well enough to do the job. Usually the companies will have very specific instructions about where and when to release the mites posted on their websites, so you can read the instructions and see whether or not you have suitable conditions before you buy.
posted by Spathe Cadet at 12:10 PM on May 12, 2019 [4 favorites]

Not sure what natural sprays you've tried, but neem oil mixed with water and a little soap killed my spider mites but good. They had huge webs all over my asparagus ferns and I just sprayed the bejesus out of them every couple of days for a few weeks. The mites are gone, and those plants are still alive and doing fine.
posted by phoenixy at 11:55 PM on May 12, 2019

You could try taping a clear plastic bag over the plant, sealing it well, and leaving it to sit for a couple of days. This should starve the mites of oxygen without harming the plants.
posted by Enid Lareg at 10:30 AM on May 13, 2019

Plastic bags over the plants might help specifically in combination with predatory mites, because they would raise the humidity around the plants. Tenting plants would also help prevent spider mites from traveling to any plants they haven't already infested, if there are any, and predator mites wouldn't be able to unproductively wander away quite as easily.

(The air in the tent will contain oxygen either way; plants take up carbon dioxide and produce oxygen even when they're being consumed by spider mites. At night, the situation is reversed, but they only suck up a little of the oxygen at night.)

Neem oil has advantages over "white oil" (vegetable oil mixed with a little dishwashing liquid and water, then shaken hard to create an emulsion; the DIY stuff works better than over-the-counter oils for me, though both are hit or miss), in that it's both an asphyxiant and a pesticide (specifically azadirachtin). Both white and neem have odors -- white oil when the vegetable oil has sat on the plants long enough to become rancid, and neem has an intrinsically strong smell (Wikipedia nails the description: "a rather strong odor that is said to combine the odours of peanut and garlic"). The first three or four times I sprayed neem oil on anything, I came very close to retching, so start with one plant and see how that goes before you treat the others.

Not everyone reacts the way I did to the smell, and even the people who do can get used to the smell. At least partly.

Also you're not supposed to spray neem oil on plants in direct sunlight (the packaging will probably warn about this), so do it at a time when you could stick the plants on the balcony for a few hours if you need to (e.g. around sunset).

There are deodorized versions of neem that contain only the azadirachtin in an odorless carrier, which I have found less effective than straight-up neem oil and only recommend if you find neem smell so unpleasant that you can't use it. (They're probably better than nothing.)
posted by Spathe Cadet at 5:09 PM on May 13, 2019

I’ve struggled with indoor spider mites for years before I finally relented and brought the tree outside to live (I have the room and climate that makes this an option). No matter how effective the natural treatments were, the mites always came back. If I had to do it again, I’d go straight to a systemic pesticide. You can get granules or liquid and the poison goes through the plant itself. It doesn’t harm the plant, but kills the pests, even hidden reservoir populations. I don’t use them outside as they also kill pollinators, but inside is fine. Bonide makes a very effective one.
posted by quince at 8:47 AM on May 14, 2019

Systemic miticides exist, but the active ingredient in most over the counter systemic pesticide granules is imidacloprid, and the exceptions mostly come from the same chemical family, the neonicotinoids. Neonicotinoids work on insect-specific receptors and don't do anything against mites (which are not insects).[1]

So read the label first, to confirm that the active ingredient will work against mites. (There will be a small-print list somewhere on the product listing all the pests that it can be expected to control: if you don't see spider mites, especially "two-spotted spider mite," listed, that's the label telling you it's not going to do anything.)

After searching on line for half an hour or so, I could only find two chemicals which are approved systemic miticides, acephate and spirotetramat. Bonide makes an OTC version of acephate, but the label goes out of its way to avoid claiming it will eliminate mites;[2] I couldn't find an OTC spirotetramat at all.

Some products are not safe to use indoors.[3] (I declined to link the Bonide product because it is explicitly outdoors-only.[4]) If the label doesn't say that you can use it indoors and provide specific directions for how to do that, you probably shouldn't.


[1] In fact, several years ago I remember seeing the claim that plants treated with imidacloprid become more appealing to spider mites, though I can't find this now and I don't remember who was making the claim so it is possibly bullshit.
[2] ". . . spittlebug, sunflower moth, tent caterpillars, two spotted spider mite (suppression), webworms, willow leaf beetle . . . "
[3] In particular, organophosphates are harmful to mammals as well as bugs, and you should not be breathing them in, in an enclosed space, for days at a time. (Guess what class of pesticide acephate is?)
[4] Bonide's website lists a total of ten products for houseplants. Only two have labels claiming effectiveness against spider mites.
The active ingredients of one are cottonseed oil, clove oil, and garlic oil, which I have tried repeatedly in multiple contexts and promise is absolutely useless against real-world spider mites.
The active ingredients of the other are pyrethrins (insect-specific; not effective against mites) and sulfur (not a systemic, and I am deeply skeptical it does anything for spider mites at all, but it's super annoying so maybe. Sulfur is primarily a fungicide, horticulturally speaking.).
posted by Spathe Cadet at 5:11 PM on May 14, 2019

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